InterPro

Pentaxins (or pentraxins) [PMID: 6356809, PMID: 7772283] are a family of proteins which show, under electron microscopy, a discoid arrangement of five noncovalently bound subunits. Proteins known to belong to this family are:

• C-reactive protein (CRP), a protein which, in mammals, is expressed during acute phase response to tissue injury or inflammation. CRP displays several functions associated with host defense: it promotes agglutination, bacterial capsular swelling, phagocytosis and complement fixation through its calcium-dependent binding to phosphorylcholine. CRPs have also been sequenced in an invertebrate, the Atlantic horseshoe crab, where they are a normal constituent of the hemolymph.
• Serum Amyloid P-component (SAP), a precursor of amyloid component P which is found in basement membrane and is associated with amyloid deposits.
• Hamster female protein (FP), a plasma protein whose concentration is altered by sex steroids and stimuli that elicit an acute phase response.

A number of proteins, whose function is not yet clear, contain a C-terminal pentaxin-like domain. These proteins are:

• Human PTX3 (or TSG-14). PTX3 is a cytokine-induced protein.
• Guinea pig apexin [PMID: 7798266], a sperm acrosomal protein. Apexin seems to be the ortholog of human neuronal pentraxin II (gene NPTX2) [PMID: 8530029].
• Rat neuronal pentaxin I [PMID: 7695898].

The sequences of the different members of this family are quite conserved. This entry represents a six residue pattern which includes a cysteine known to be involved in a disulfide bridge in CRPs and SAP.